Such devices as mentioned above have hitherto been known, and as an instance thereof, there can be cited a device disclosed previously by the applicant of the present invention in Japanese Patent application No. 37699/1978 (Laid-open Application No. 129558/1979) hereinafter referred to as the previous invention. To begin with, said previous invention will be explained with reference to FIGS. 1 through 3 of the appended drawings.
Among the reference numerals in these drawings, 1 denotes a vacuum chamber, which is provided with an exhaust port 2 disposed on the top and a discharge port 3 for taking out the crushed dried product disposed on the bottom. Upper and lower belt conveyers 6 for conveying the material being dried are arranged in multistage fashion and each belt is stretched between a driving roll 4 and a guide roll 5 to move in the direction of the arrow. The return stroke side of each belt is disposed spaced from the feed stroke side. This belt 6 is desirably made of glass cloth coated with polytetrafluoroethylene and subjected to surface treatment for electrostatic charge prevention. Heaters 7 are disposed below the lower face of each belt 6 and above the upper face of the uppermost belt 6 by leaving spaces between the belts. Above the uppermost heater 7 and under the lowermost heater 7 there are disposed reflectors 8 respectively. On the upper face of each belt 6, there is provided a feed nozzle 9 for the material to be dried disposed ahead of the heater 7 along the direction of movement of the belt. To the rear of the heater 7 there are provided a crushing roll 10 disposed to correspond to a belt supporting base 11 installed on the lower face of each belt 6 and an angle scraper 12 for the purpose of scraping the crushed, dried material from the surface of the belt 6 and removing it to both sides of said belt. On both sides of each belt 6 there is provided a guide plate 13 respectively in armor-sleeve fashion in order to prevent the crushed, dried material from attaching to the lower face of the belt 6.
In addition to the above described previous invention, there is known another device such as shown in FIG. 4 which has also been developed by the present inventors. This invention is, so to speak, a modification of the previous invention, wherein a different crushing/discharging device is installed instead of the crushing roll 10, belt supporting base 11, scraper 12 and discharge port 3 of the device of the previous invention. (This modification is hereinafter referred to as the `previous proposition`.) Details of this invention will be explained in the following.
In this crushing/discharging device, a rotary cutter 10' is disposed above the driving roll 4 for the belt 6, and this cutter 10' is always being pulled in the direction of the driving roll 4 by means of a spring 14 in order to crush a matlike dried material moving along the belt 6 as it rotates.
The dried material crushed in this way is scraped off by a scraper 12' installed to the rear of the cutter 10', collected by a ductlike chute 13' and allowed to fall down.
The dried material thus fallen is collected into a collecting hopper 16 disposed at the lower opening of the chamber 1. In this hopper 16 there is provided a rotary cutter 19 having a perforated metal retainer 18 around it which is driven by an air motor 17. The dried material thus collected into the hopper 16 is crushed by the rotary cutter 19 and, after having been regulated in grain size by passing through the perforated metal retainer 18, is taken out of the apparatus.
In the case of such a crushing device, however, when the matlike dried material 15 is too thick, said dried material 15 may pass over the cutter 10', and when the hardness of the material is too high, the material may lift the cutter 10', whereby the device may fail to fulfil its function of crushing. Therefore, in order to avoid such troubles, it is necessary to enhance the diameter of the cutter 10', increase the strength of the spring 14, and so on.
Moreover, in the case of this device, inasmuch as the crushing is to be carried out on the belt 6, there occurs a phenomenon of return of fine particles, resulting in the mixing of scorched particles in the final product. And, in fact, it is impossible to remove effectively fine particles having a diameter of less than 30.mu. by means of the scraper 12'. The reason is that is is difficult to improve the precision of working of the scraper 12' to the extent of enabling it to perform such removal, and the same goes with respect to the precision of finishing of the surface of the belt 6.
Further, in the case of this device, when the dried material 15 is hard, there is a fear of impairing the surface of the belt 6 at the time of crushing the material coarsely, and as the angle of inclination .alpha. of the chute 13' to collect the crushed, dried material is determined by the ratio H/L of the width L of the belt 6 to the height H of the driving roll 4 relative to the returning belt 6, the lower a belt 6 is disposed, the smaller becomes the angle of inclination .alpha., resulting in lowering of efficiency in conveying the crushed material. Therefore, the height H of the driving roll 4 relative to the lowermost returning belt 6 is naturally limited. Accordingly, in order to enhance the conveying efficiency in conformity with an increase in the number of stages, provision of a bulky vacuum chamber with large size on the side of the product discharge port is required. As a countermeasure, it is conceivable to install a vibrator or the like on each stage of the chute 13, but provision of an electric motor within the vacuum chamber makes it difficult to radiate heat generated by the motor and damages the apparatus, so it is common not to take such a measure.
Compared with this device illustrated in FIG. 4, the previous invention is superior in several points but is the same with the former in so far as it is devised to perform the work of coarsely crushing and scraping on the surface of the belt 6 and is incapable of checking the occurrence of the phenomenon of return of fine particles. Besides, this method would cause fine particles to float within the vacuum chamber 1 and attach to the back of the belt 6, the belt supporting roll, etc., causing meandering of the belt 6. Further, disposition of many guide plates 13 along both sides of the belt 6 requires the provision of an unexpectedly large capacity of the vacuum chamber 1 on the side of the discharge port for the crushed dried material. Accordingly, the present invention is intended to provide a device that can make up for the defects inherent in the fore going previous devices by improving them on the basis of the following conceptions in order to produce dried products of good quality stably and continuously:
(1) Dried materials that have attained a prescribed moisture are to be scraped, coarsely crushed, conveyed and thereafter discharged to the outside of the vacuum system through the popular processes of collection of powder, regulation of grain size and discharge of product. PA1 (2) The works steps of coarsely crushing and scraping are not to be carried out on the surface of the belt. PA1 (3) The dried materials scraped from the surface of belt and crushed are to be conveyed and collected without fail and should not cause floating of fine particles and the like. PA1 (4) The space for installing the device is to be minimized so as to facilitate maintenance and control thereof, including washing.